In general, the invention relates to data processing. In particular, the invention relates to data processing in quasi-cyclic low density parity check (QC-LDPC) decoders.
With the continuing demand for high-reliability transmission of information in digital communication and storage systems, and with the rapid increase in available computational power, various coding and decoding techniques have been investigated and applied to increase the fidelity of these systems. One such coding technique, low-density parity check (LDPC) coding, was first proposed in the 1960s, but was not used until the late 1990s when researchers began to investigate iterative coding and decoding techniques.
LDPC codes form a class of linear block codes that are of particular interest due to their capability of approaching the Shannon limit for channel capacity. LDPC coding techniques are generally iterative in nature, and can be represented by many different types of parity check matrices. The structure of an LDPC code's parity check matrix can be, for example, random, cyclic, or quasi-cyclic. LDPC codes defined by quasi-cyclic parity check matrices are particularly common and computationally efficient. These codes are known as quasi-cyclic low density parity check (QC-LDPC) codes.
The performance capability of a coding scheme, such as a LDPC coding scheme, is often described by the code's performance curve, which is a plot of signal-to-noise ratios (SNR) vs. Bit Error Rate (BER) or Sector Error Rate (SER). The performance curve of LDPC codes generally consists of two regions: the waterfall region and the error floor region (see FIG. 3). In the waterfall region, the code's BER or equivalently, SER, decreases rapidly with improvements in SNR. However, in the high SNR operating region, the BER/SER disadvantageously plateaus to an error floor, meaning that further improvements in channel condition would not lead to lower BER/SER. Although the error floors of well designed LDPC codes are generally low, they might not be acceptable for communication channels that must guarantee high degree of data reliability.